1. Field of the Invention
The present invention relates to tuning fork-type vibrators, tuning fork-type vibrator manufacturing methods, and angular velocity sensors and, more particularly, to a tuning fork-type vibrator used to detect an angular velocity in an angular velocity sensor, a method of manufacturing the tuning fork-type vibrator, and an angular velocity sensor including the tuning fork-type vibrator.
2. Description of the Related Art
FIG. 11 is a perspective view of an example of a tuning fork-type vibrator in the related art. A tuning fork-type vibrator 1 includes a vibrating body including a rectangular base 2a and two legs 2b and 2c extending from one end of the base 2a in parallel to each other. The vibrating body includes two fork-type piezoelectric substrates 3a and 3b. An intermediate metal layer 4 is disposed between the piezoelectric substrates 3a and 3b. Three electrodes 5a, 5b, and 5c are arranged on the surface of the piezoelectric substrate 3a. The electrodes 5a, 5b, and 5c are separated from one another by two separating portions extending linearly from the base 2a to the legs 2b and 2c. An entire-surface electrode 6 is arranged on the surface of the vibrating body 3b. In the tuning fork-type vibrator 1, the piezoelectric substrates 3a and 3b are polarized in opposite directions along the thickness thereof.
The tuning fork-type vibrator 1 is attached to a circuit board. At that time, the three electrodes 5a, 5b, and 5c on the piezoelectric substrate 3a are mechanically and electrically connected to electrodes provided on the circuit board by a conductive adhesive. A driving circuit is connected between the electrode 5b, which is the middle one of the three electrodes 5a, 5b, and 5c on the piezoelectric substrate 3a, and each of the outer electrodes 5a and 5c. A detection circuit for detecting a rotational angular velocity is connected to the outer electrodes 5a and 5c. The driving circuit vibrates the legs 2b and 2c in the tuning fork-type vibrator 1 so that they move toward and away from each other. At that time, since the legs 2b and 2c move in the same direction with respect to the direction of polarization, the electrodes 5a and 5c connected to the detection circuit output the same signal. When the detection circuit calculates the difference between signals output from the electrodes 5a and 5c, the difference therefore becomes zero.
In this state, when a rotational angular velocity about a central axis between the legs 2b and 2c is applied, a Coriolis force is applied to the legs 2b and 2c along an axis perpendicular to the direction of vibration. Since the legs 2b and 2c move toward and away from each other in the fundamental vibration, the directions of Coriolis forces applied to the legs 2b and 2c are opposite to each other. Accordingly, the legs 2b and 2c move in opposite directions along an axis perpendicular to the direction of fundamental vibration. These movements of the legs 2b and 2c change output signals from the two electrodes 5a and 5c in opposite phases. When the detection circuit calculates the difference between these output signals, the detection circuit obtains a signal corresponding to the rotational angular velocity (see, for example, Japanese Patent No. 3969459).
In the tuning fork-type vibrator, three electrodes used to drive and detect are provided on one of the piezoelectric substrates. When the widths of the separating portions between electrodes are narrow and the electrodes on the piezoelectric substrate are connected to the electrodes on the circuit board by a conductive adhesive, the electrodes may become short circuited by the conductive adhesive and the insulation reliability is reduced. When the widths of the separating portions between electrodes are increased, the areas of the electrodes on the legs are reduced. As a result, the driving efficiency of the tuning fork-type vibrator and the outputting efficiency of a signal generated by the movements of the legs are reduced. This leads to a reduction in the sensitivity of the tuning fork-type vibrator and a degradation in an S/N ratio.